1. Field of the Invention
The present invention relates to a sheet conveying apparatus and an image forming apparatus including the same.
2. Description of the Related Art
In general, the accuracy of a recording position (hereinafter, also referred to as “recording precision”) of an image with respect to a sheet is one of the important factors from the viewpoint of keeping the quality in image formation. In order to enhance the recording precision in an image forming apparatus, when a sheet to be conveyed is skewed, it is necessary to correct the skewed sheet. Therefore, in conventional image forming apparatus, there have been proposed various sheet conveying apparatus having a skew feed correction function so as to enhance the recording precision.
In the sheet conveying apparatus disclosed in Japanese Patent Application Laid-Open No. H09-183539, a plurality of conveying roller pairs are provided in a sheet width direction orthogonal to a sheet conveying direction, and a restraining member that is rotatable about a rotary shaft of the conveying rollers is disposed between the conveying roller pairs. The restraining member has an abutment surface where a sheet abuts. When the leading edge of a sheet abuts against the abutment surface, the sheet slacks due to the reaction force from the abutment portion to form a curved loop. The formation of the loop aligns the leading edge of the sheet in parallel to the sheet width direction orthogonal to the conveying direction to correct a skew. Then, when the restraining member is rotated, the leading edge of the sheet is nipped by a nip portion of the conveying roller pairs while being aligned in parallel to the sheet width direction, and thus the sheet is conveyed. That is, the sheet is conveyed with the skew thereof corrected. By the way, in recent years, there is a demand for an image forming apparatus capable of performing printing to various media. In particular, there is an increasing demand for printing on a sheet with a basis weight smaller than those of the conventional sheets (for example, a sheet of less than 60 g/m2, also referred to as “thin sheet”) so as to achieve further resource saving. However, the conventional sheet conveying apparatus as described above may not perform skew feed correction sufficiently with respect to a thin sheet.
For example, in skew feed correction of a thin sheet, by the time when a sheet is nipped by the conveying rollers after abutting against the restraining member, a portion abutting the abutment portion of the restraining member is deformed locally, and the leading edge of the sheet may not be kept straight. As a result, the reaction force from the abutment portion is less transmitted in the conveying direction of the sheet, and the above-mentioned curved loop to be required for correcting the skew of the sheet is hard to be formed, which degrades the precision of skew feed correction. The local undulating state of the leading edge of the sheet is more conspicuous as the basis weight of the sheet is smaller (the stiffness of the sheet is smaller), and the leading edge of the sheet may be bent locally.